1. Field of the Invention
The present invention relates to a developing device applied to image formation apparatuses such as photocopiers, printers, and facsimile devices and the like, and to an image formation apparatus and a process cartridge comprising the same, and further relates to a configuration for adjusting the environmental atmosphere which affects charging properties of developing agent, and preventing soiling due to scattering of developing agent.
2. Discussion of Background Art
Generally, in order to prevent scattering of toner within an image formation apparatus, the interior of the developing device and the outside are isolated one from another by a casing, except for an opening whereby a portion of the surface of a developing agent carrying member is made to face a latent image carrying member. With this structure, a gap exists between the surface of the latent image carrying member and the casing, at the opening. Accordingly, there is the possibility that toner within the developing agent might scatter outside of the developing device through this gap. In the event that toner scatters outside of the developing device, recording media such as paper or the like upon which images are to be ultimately formed may be soiled due to the toner which has spread throughout the image formation apparatus, or normal actions of members and devices disposed within the image formation apparatus may be inhibited. Accordingly, suppressing scattering of toner outside of the developing device is an extremely important issue.
Such scattering of toner primarily occurs at a gap existing upstream in the direction of rotation of the developing agent carrying member (hereafter, referred to simply as “upstream side”) of the developing region where the developing agent carrying member and latent image carrying member face one another, and a gap existing downstream in the direction of rotation of the developing agent carrying member (hereafter, referred to simply as “downstream side”) thereof.
A developing device disclosed below is known, for example, as an arrangement for suppressing scattering of toner occurring at, of the above, the gap existing at the downstream side. With this developing device, a carrier collecting roller is provided downstream from the developing region, and the width of a first gap which is the gap between the developing agent carrying member and the carrier collecting roller is set so as to be larger than the width of a second gap which is a gap between the developing agent carrying member and the latent image carrying member. In the space encompassed by the latent image carrying member and developing agent carrying member and carrier collecting roller, air enters and exists from the three places of the first gap, the second gap, and a third gap which is a gap between the carrier collecting roller and the latent image carrying member. With this developing device, a magnetic brush is formed by the developing agent bristling on the surface of the developing agent carrying member, and passing through the first gap and the second gap accompanying the rotation of the developing agent carrying member in this state. At this time, each of the magnetic brushes act as slender and small propellers, such that air between the developing agent particles making up the magnetic brushes moves due to the magnetic brushes moving. Accordingly, a strong airflow is generated at the first gap and the second gap in the direction of rotation of the developing agent carrying member. On the other hand, at the third gap, there is little air following the rotation of either the carrier collecting roller and the latent image carrying member, so any airflow generated by the rotations thereof is weak. Accordingly, the airflow at this third gap is determined almost dependently on the airflow generated at the first gap and the second gap. Specifically, difference between the amount of the airflow which flows into the space through the second gap and the amount of the airflow which flows out through the first gap is the airflow generated at the third gap. With this developing device, the width of the first gap between the developing agent carrying member and the carrier collecting roller is set so as to be wider than the width of the second gap between the developing agent carrying member and the latent image carrying member. Accordingly, the airflow flowing out from the space through the first gap is greater than the airflow which flows into this space through the second gap, so the air pressure in this space drops, and acts to suction air in through the third gap. This means that an airflow is generated at this third gap which heads toward the space. This airflow is intended to suppress scattering of toner which occurs downstream of the developing region as discussed in Japanese Unexamined Patent Application Publication No. 10-3220.
On the other hand, for example, a developing device disclosed below is known as an arrangement for suppressing scattering of toner occurring at the gap existing at the upstream side. With this developing device, a partitioning member is provided between the developing agent carrying member and casing at the upstream side, for partitioning between these. With this developing device, rotation of the developing agent carrying member transports developing agent to the developing region, restricted to a predetermined thickness by a developing agent restricting member. The partitioning member is placed somewhere between the developing agent restricting member and the developing region. The space adjacent to the downstream side of the developing agent restricting member in the direction of rotation of the developing agent carrying member (doctor-adjacent space), and the gap existing on the upstream side, communicate through the two channel spaces of the space encompassed by the partitioning member and the casing (first channel space), and the space encompassed by the partitioning member and the developing agent carrying member (second channel space). According to the Document disclosing this arrangement, an airflow is generated at the second channel space following the surface of the developing agent carrying member in accordance with rotations of the developing agent carrying member. Developing agent is present at a high density at the gap between the developing agent restricting member and the developing agent carrying member (doctor gap), and accordingly, airflow through this doctor gap is poor. Consequently, negative pressure is generated at the doctor-adjacent space. Accordingly, air flows into the doctor-adjacent space through the first channel space, so an airflow heading toward the doctor-adjacent space from the gap at the upstream side is generated in the first channel space. Thus, toner floating at the upstream side of the developing region is transported to the doctor-adjacent space by this airflow, which intends to suppress scattering of toner from the gap at the upstream side to the outside of the developing device as discussed in Japanese Unexamined Patent Application Publication No. 63-159887.
Further, in order to prevent scattering of toner within the image formation apparatus, general developing devices have a structure wherein the inside of the developing device and the outside thereof are isolated one from another through the casing except for the opening portion where a portion of the surface of the developing agent carrying member faces the latent image carrying member. With such a construction as well, a gap exists between the surface of the latent image carrying member and the casing. Accordingly, there is the possibility that toner within the developing agent might scatter outside of the developing device through this gap. In the event that toner scatters outside of the developing device, toner spreading within the image formation apparatus may soil recording media such as paper or the like upon which images are to be ultimately formed, or normal actions of members and devices disposed within the image formation apparatus may be inhibited, for example. Accordingly, suppressing scattering of toner outside of the developing device is an extremely important issue.
Such scattering of toner primarily occurs at a gap existing upstream in the direction of rotation of the developing agent carrying member (hereafter, referred to simply as “upstream side”) of the developing region where the developing agent carrying member and latent image carrying member face one another, and a gap existing downstream in the direction of rotation of the developing agent carrying member (hereafter, referred to simply as “downstream side”) thereof. Of these, the gap at the upstream side can be closed off by employing a configuration wherein, for example, a sheet member attached to the end portion of the casing forming the gap comes into contact with the surface of the latent image carrying member. Accordingly, scattering of toner occurring at the gap on the upstream side can be readily suppressed. Conversely, the gap at the downstream side cannot be closed off with a sheet member using such a configuration. The reason is that generally, the latent image carrying member and the developing agent carrying member rotate such that the surfaces of each are moving in the same direction at the position of closest proximity, and a toner image adheres to the surface portion of the latent image carrying member downstream from the developing region, so scattering of toner occurring at the gap on the downstream side has conventionally been a difficult problem.
As a method for solving this problem, a developing device has been proposed wherein an electroconductive roller is provided within the developing device downstream of the developing region, with the electroconductive roller rotating in a direction such that the surfaces of the electroconductive roller and the developing agent carrying member are moving in the same direction at the position of closest proximity. According to the description in the Document disclosing this arrangement, an airflow is generated by the electroconductive roller and the developing agent carrying member rotating so as to be moving in the same direction at the position of closest proximity. Accordingly, a flow of air which passes from the space surrounded by the developing agent carrying member and latent image carrying member and electroconductive roller, through the space between the developing agent carrying member and the electroconductive roller, into the developing device, is formed. The toner scattered and floating in the space at the developing region is guided into the developing device by this flow of air, which is intended to suppress scattering of toner from occurring at the downstream side of the developing region as discussed in Japanese Unexamined Patent Application Publication No. 5-66663.
A developing device has been proposed wherein a carrier collecting roller is provided downstream of the developing region, and wherein the width of the first gap which is the gap between the developing agent carrying member and the carrier collecting roller is formed wider than the width of a second gap which is the gap between the developing agent carrying member and the latent image carrying member. This developing device has airflow generating means, for generating an airflow at a third gap which is the gap between the carrier collecting roller and the latent image carrying member, from outside of the developing device to the inside thereof. In the space surrounded by the latent image carrying member and the developing agent carrying member and the carrier collecting roller, the air enters and exits from the places of the first gap, the second gap, and the third gap. With this developing device, the developing agent bristles on the surface of the developing agent carrying member at the first gap and the second gap so as to form a magnetic brush, and passes through accompanying the rotation of the developing agent carrying member in this state. At this time, each of the magnetic brushes act as slender and small propellers, such that air between the developing agent particles making up the magnetic brushes moves due to the magnetic brushes moving. Accordingly, a strong airflow is generated at the first gap and the second gap in the direction of rotation of the developing agent carrying member. On the other hand, at the third gap, there is little air following the rotation of either the carrier collecting roller and the latent image carrying member, so any airflow generated by the rotations thereof is weak. Accordingly, the airflow at this third gap is determined almost dependently on the airflow generated at the first gap and the second gap. Specifically, difference between the amount of the airflow which flows into the space through the second gap and the amount of the airflow which flows out through the first gap is the airflow generated at the third gap. With this developing device, the width of the first gap between the developing agent carrying member and the carrier collecting roller is set so as to be wider than the width of the second gap between the developing agent carrying member and the latent image carrying member. Accordingly, the airflow flowing out from the space through the first gap is greater than the airflow which flows into this space through the second gap, so the air pressure in this space drops, and acts to suction air in through the third gap. This means that an airflow is generated at this third gap which heads toward the space. This airflow is intended to suppress scattering of toner which occurs downstream of the developing region as discussed in
Japanese Unexamined Patent Application Publication No. 10-3220.
Also, a developing device has been proposed having a configuration wherein the viscous airflow downstream of the developing region acts effectively to generate an airflow heading into the developing device, comprising a filter member for venting the viscous airflow which has flowed into the developing device. According to the Document disclosing this arrangement, the viscous airflow flowing into the developing device is externally vented through the filter member, so the inner pressure within the developing device rises and becomes saturated due to the viscous airflow, thereby conversely enabling an airflow blowing out at the downstream side of the developing region to be prevented. According to this device, no airflow blowing out at the downstream side of the developing region is generated, so an airflow heading into the developing device is perpetually generated, and a stable viscous airflow (suctioning airflow) can be generated at the downstream side of the developing region, thereby enabling stable suppressing of scattering of the toner generated at the downstream side of the developing region as discussed in Japanese Unexamined Patent Application Publication No. 2002-244432.
Though this is not clear regarding the developing device described in Patent Document 3, the developing devices described in Patent Document 4 and Patent Document 5 have structures wherein external air can flow into inner space of the casing through a gap (inlet gap) formed between the downstream edge portion of an opening for exposing the developing agent carrying member and the surface of the latent image carrying member. The airflow flowing in through the inlet gap suppresses scattering of the toner outside of the developing device.
Also, with image formation apparatuses such as photocopiers or printers or facsimile apparatuses or printing apparatuses, there are configurations wherein the latent image carrying member, and of the devices used for the image formation processing, a charging device, developing device, and/or cleaning devices are stored together to form a process cartridge, which is used to transfer a visible image formed on the photosensitive member which is the latent image carrying member onto a recording sheet such as paper or the like, by means of a transfer device disposed nearby the process cartridge, thereby obtaining a copied article.
It is known that in the event of performing visual image processing for an electrostatic latent image formed on the photosensitive member which is the latent image carrying member, the charging properties of the developing agent supplied affect the image concentration and gradient reproducibility, and further it is known that charging properties are readily affected by the environmental ambient atmosphere, humidity in particular. Further, in the event that discharge products such as NOx and the like formed by discharge, which is one of the methods carried out in the charging step, accumulates on the surface of the latent image carrying member, the charging properties and photosensitivity properties deteriorate, which tends to lead to deterioration in latent image carrying and so forth.
In order to solve such inconveniences, a configuration has been proposed wherein air subjected to humidity adjustment is supplied into the developing device as discussed in Japanese Unexamined Patent Application Publication No. 6-19293.
Also, the developing agent carried by the developing sleeve within the developing device is brought into contact with the photosensitive member in the state that the portion of the developing device facing the photosensitive member which is the latent image carrying member is opened to the atmosphere, but the air near the surface of the photosensitive member and the developing sleeve following the rotation thereof due to viscosity, and create a following airflow. Accordingly, the developing agent moving within the developing device may scatter toner due to reduction of pressure at the portion opened to the atmosphere, owing to the following airflow being released.
Conventionally, configurations for preventing scattering of toner have included a configuration wherein the interior of the developing device is shielded by bringing an elastic seal or the like into contact with the position on the developing sleeve which has passed the position of supplying developing agent to the photosensitive member, and a configuration comprising an electroconductive roller which can perform electrostatic adsorption of toner scattered on the perimeter of the developing sleeve which has passed the developing position and toner which would scatter from the opening as discussed in Japanese Unexamined Patent Application Publication No. 5-66663.
On the other hand, as a configuration for preventing scattering of toner due to toner being blown out owing to increased pressure within the developing device from the following airflow generated accompanying the movement of the photosensitive member and the developing sleeve, there is a configuration wherein an exhaust unit is provided partway along the channel where the developing agent which has separated from the developing sleeve flows as discussed in
Japanese Unexamined Patent Application Publication No. 2002-244432.
Also, with image formation apparatuses such as photocopiers or printers or facsimile apparatuses or printing apparatuses, visible image processing is performed by developing an electrostatic latent image formed on a photosensitive member used as a latent image carrying member with toner in a developing agent.
One-component or two-component developing agents are used with developing devices, and with either developing agent, a developing sleeve which is the carrying member for the developing agent, a developing agent stirring/mixing member, and further a layer thickness restricting member for restricting the thickness of the developing agent, are provided, and these components are disposed within a housing forming the shell of the developing device.
The developing sleeve is arranged so that a portion of the surface thereof is exposed from an opening provided to the housing, thereby bringing the developing agent on the surface thereof into contact with the photosensitive member.
Now, it is known that in the event of performing visible image processing wherein an electrostatic latent image formed on a photosensitive member is developed, the charging properties of the developing agent supplied affect the image concentration and gradient reproducibility. One of the factors causing change in the charging properties of the developing agent is the environmental ambient atmosphere, humidity in particular.
On the other hand, as for inconveniences occurring at the time of forming images, there are adverse effects of discharge products generated at the time of charging the photosensitive member. That is to say, in the event that discharge products such as NOx and the like adhere to the surface of the photosensitive member, the charging properties and photosensitivity properties are affected, leading to deterioration of the photosensitive member.
In order to solve such inconveniences, a configuration has been proposed wherein air subjected to humidity adjustment is supplied into the developing device as discussed in Japanese Unexamined Patent Application Publication No. 6-19293.
Further, the configuration of the developing device is such that a developing sleeve, a developing agent stirring/mixing member, and a layer thickness restricting member for restricting the thickness of the developing agent, are stored within a housing, with only a part of the developing sleeve exposed outwards, but the a developing sleeve and the developing agent stirring/mixing member are rotational members, and accordingly members which drag air at the surface layer portion thereof due to the rotations thereof and generate airflow. This changes the pressure within the housing, and due to a tendency to particularly become high pressure, residual toner carried on the developing sleeve following passing through the developing region configured at the portion facing the photosensitive member may scatter out from the opening of the housing, due to the increased pressure within the housing. Scattering of toner from the housing side results in inviting soiling of peripheral units, primarily the photosensitive member. Also, as a configuration for preventing scattering of toner on the developing sleeve following passing through the developing region, there is a configuration wherein the gap between the wall of the housing at the position where the developing sleeve is stored which faces the developing sleeve, and the developing sleeve, is formed greater than the gap between the wall of the housing and the photosensitive member at the position where the photosensitive member faces the wall of the housing as discussed in Japanese Unexamined Patent Application Publication No. 11-7191.
In this configuration, the toner on the developing sleeve which has passed through the developing region is readily taken into the housing using the tendency for the pressure therein to become negative, due to the increase in area occurring at the time of reaching the gap between the developing sleeve and the housing wall, which is set so as to be wider than the gap between the developing sleeve and the photosensitive member.
Further, separately from this configuration, there is a configuration wherein a carrier collecting roller is provided at a position behind the developing sleeve in the direction of movement of the photosensitive member, with the carrier collecting roller being set so as to rotate in a direction such that the portion thereof facing the developing sleeve moves in the same direction at that position, and with the gap between the carrier collecting roller and the photosensitive member at the portion facing one another being used as a gap through which air can flow as discussed in Japanese Unexamined Patent Application Publication No. 10-3220.
With this configuration, the airflow generated by rotations of the carrier collecting roller is set as the direction in which air flows through the gap where the carrier collecting roller faces the photosensitive member, by creating the tendency for the pressure to become negative at the facing gap, thereby sucking the toner which has passed through the developing region into the housing.
With the developing device disclosed in Patent Document 1, developing agent carried out the surface of the developing agent carrying member is restricted to a predetermined thickness by a developing agent restricting member due to the developing agent carrying member rotating, and thus is transported to the developing region. A fixed magnet is disposed within the developing agent carrying member at the portion from the developing agent restricting member to the developing region. Accordingly, in the space surrounded by the inner casing wall and surface of the developing agent carrying member from the developing agent restriction member to the developing region (developing agent transporting space), the developing agent bristles.
As described above, upon the developing agent on the rotating developing agent carrying member bristling, each of the magnetic brushes thereof act as propellers, such that a strong airflow is generated following the surface of the developing agent carrying member, in the direction of rotation of the developing agent carrying member. That is, a strong airflow facing the gap at the upstream side from the developing agent restricting member side is generated in the developing agent transporting space. This strong airflow causes a great amount of gas to enter into the space encompassed by the surface of the developing agent carrying member and the casing inner wall from the developing agent bristling position to the developing region (upstream space), so the pressure increases at the upstream space. Accordingly, in the event that the only way of escape from this upstream space that the gas has is the gap at the upstream side, a strong airflow is generated from the gap at the upstream side toward the outside of the developing device, and toner scattering occurs due to this airflow.
With the developing device disclosed in Patent Document 1, a gap large enough for air to flow through (gas flow space) is formed in the developing agent transporting space, between the tip of the magnetic brush formed of the bristling developing agent and the inner wall of the casing as discussed in Japanese Unexamined Patent Application Publication No. 10-3220. Also, the space adjacent to the downstream side of the developing agent restricting member in the direction of rotation of the developing agent carrying member (doctor-adjacent space) becomes negative pressure in the same way as the developing device disclosed in Patent Document 2, so the gas from the upstream space might seem to be capable of escaping to this doctor-adjacent space besides the gap at the upstream side. However, with the developing agent transporting space, the airflow heading toward the doctor-adjacent space through the gas flow channel, and the airflow heading toward the gap upstream from the magnetic brush, are flowing in mutually opposite directions. Moreover, the airflow heading toward the doctor-adjacent space is greatly inhibited by the viscous resistance of the airflow heading toward the gap at the upstream side, which has been generated by propeller-actions of the bristling developing agent. Accordingly, the gas within the upper space does not flow to the doctor-adjacent space very much, and consequently, almost all of this flows out of the developing device from the gap at the upstream side. Thus, the developing device disclosed in Patent Document 1 cannot be said to sufficiently suppress toner scattering occurring at the space at the upstream side.
On the other hand, with the developing device in Patent Document 2, negative pressure is generated at the doctor-adjacent space according to the description in this Document, stating that an airflow is generated in the first channel space, heading from the gap at the upstream side toward the doctor-adjacent space. In order to generate a strong airflow which can sufficiently suppress scattering of toner generated at the gap at the upstream side, the doctor-adjacent space needs to be under a powerful negative pressure. However, with the developing device according to this Document, the force acting to carrying the airflow out from this doctor-adjacent space is the flow generated accompanying the rotations of the developing agent carrying member in the second channel space, i.e., the surface layer airflow of the developing agent carrying member. The actions of such a surface layer airflow alone cannot yield a negative pressure necessary to sufficiently suppress scattering of the toner in the doctor-adjacent space. Accordingly, the developing device in this Document cannot generate a strong airflow at the gap at the upstream side, and cannot sufficiently suppress toner scattering.
Now, the intensity of the airflow flowing in through the inlet gap is greatly affected by the state of the airflow in the inner space of the casing. For example, in the event that part or all of the flow path of the external air flowing into the inner space of the casing from the inlet gap is closed off by the developing agent, the amount of gas flowing in through the inlet gap per time increment decreases. In such a case, the intensity of the airflow flowing through the inlet gap becomes smaller. This will be described below with reference to a specific example.
FIG. 40 is a schematic configuration diagram illustrating an example of a conventional developing device. The developing agent used in this developing device is made up of a magnetic carrier and a non-magnetic toner. The developing device 4380 has magnetic field generating means 4385 having multiple magnets disposed fixedly within a developing sleeve 4381 which is a developing agent carrying member. The developing agent, which has passed through a developing region where the developing sleeve 4381 and a photosensitive drum 4020 which is the latent image carrying member face one another passes through a channel space B between the inner wall of the casing 4384 and the developing sleeve 4381 in a state of being carried on the surface of the developing sleeve, and is returned to the inner space A of the casing. Subsequently, the developing agent is peeled off from the surface of the developing sleeve by a repelling magnetic field generated by mutually adjacent S-pole magnets 4385a and 4385b. This peeling occurs as follows. The developing agent T2 on the developing sleeve 4381 which has been transported to the region where it is affected by the repelling magnetic field is kept from integrally moving with the surface of the developing sleeve by this repelling magnetic field, and is retained as shown in the drawing. The retained developing agent T2 is pushed out by the new developing agent being consecutively sent by the rotations of the developing sleeve 4381, and finally falls off due to gravity, whereby peeling occurs. The developing agent T2 which is retained prior to peeling is in a quantitative equilibrium, due to the continuous running of the developing device 4380. In the example shown in the drawing, the channel space B is closed off by the developing agent T2 in this equilibrium state. Moreover, new developing agent is consecutively sent upon this retained developing agent T2, making for a highly dense state in which it is extremely difficult for air to pass through. In this way, the channel space B closed off by the developing agent T2 is a channel for external air to flow into the inner space A of the casing 4381 from the inlet gap C between the lower edge portion 4384a of the opening of the casing 4384 and the surface of the photosensitive drum 4020. Accordingly, the flow passing through this inlet gap C does not occur any more.
Also, in the event that a source for generating an airflow which would disturb the air flow, for example, exists in the inner space of the casing, the amount of gas flowing in through the inlet gap decreases per time increment, whereby the intensity of the airflow flowing through the inlet gap decreases. Describing with reference to the example of the developing device shown in FIG. 40, the developing device 4380 has two transporting screws 4382a and 4382b. The transporting screws 4382a and 4382b transporting the developing agent in mutually opposite directions, following the direction of the rotating axis of the developing sleeve 4381. Now, the developing sleeve 4381 rotates, and accordingly, a surface layer airflow generated by the viscosity of the air exists near the surface of the developing sleeve. Accordingly, in the event that the channel path B is not completely closed off by the developing agent T2, the external air which has flowed in from the inlet gap C can enter into the inner space A of the casing 4384 through the channel space B, due to the surface layer airflow. The external air which has entered the inner space A of the casing 4381 then is sent further into the inner space A by the surface layer airflow of the developing sleeve 4381. However, upon the developing agent being transported by the transporting screws 4382a and 4382b, a surface layer airflow is also generated on the surface of the developing agent being transported. The direction of flow of this surface layer airflow is a direction parallel to the rotational axis direction of the transporting screws 4382a and 4382b, i.e., a direction parallel to the rotational axis direction of the developing sleeve 4381, which is a direction orthogonal to the direction of flow of the surface layer airflow from the developing sleeve 4381. Accordingly, the airflow generated by the surface layer airflow of the developing sleeve 4381 attempting to send the external air deeper into the inner space A is disturbed by the surface layer flow of the developing agent being transported by the transporting screws 4382a and 4382b. In the event that this airflow is disturbed, the external air cannot readily be sent to the deeper part of the inner space A, meaning that the airflow within the channel space B becomes stagnant, and the magnitude of the airflow flowing in through the inlet gap C becomes small.
In this way, in the event that the airflow flowing in through the inlet gap C does not occur or the intensity of the airflow becomes small, the toner scattering suppression effects of the airflow disappear or deteriorate, causing a problem in that toner scattering cannot be sufficiently suppressed.
Examples of methods which can be conceived to solve this problem include a configuration wherein the developing agent T2 does not close off part or all of the channel space B, or removing the source of the airflow which disturbs the airflow. However, such methods require substantial changes in design of the developing device itself, or restrict the functions of the developing device.
Further, in a configuration wherein the environmental atmosphere around the photosensitive member is adjusted, particularly regarding humidity, and then introduced, exchanging air in a space where toner having a relatively low charged state is floating, in a short time without using forced exhausting means or the like, is difficult. Accordingly, using forced airflow generating means such as a pump or the like may be conceived, but this configuration increases the pressure within the developing device, and consequently invites scattering of toner.
On the other hand, in the event of providing an exhausting mechanism for preventing scattering of toner, this is relatively effective in cases wherein the airflow is simple in motion, such as in cases wherein the stirring means using a paddle or the like which become the source of the airflow within the developing device is singular, but in the event of using stirring means configured of multiple screw augers in order to deal with reduction in size which is in demand in recent years, the airflow generated by the stirring means is not simple since the direction of moving of the developing agent is orthogonal to the direction of motion of the developing sleeve, and for example, generating an airflow at the stirring means in the direction of suctioning the toner which is beginning to scatter becomes difficult, and sufficient suctioning cannot be performed since the pressure for suctioning is weak, and consequently, scattering of the toner cannot be completely suppressed.
Causes inviting increased pressure within the developing device other than the airflow generated by the stirring means, include the air viscously adhering to the developing agent. Viscously adhering air exists around the developing agent, and there is a portion where the amount of air increases along with the movement of the developing agent within the developing device which is a closed-off space except for one portion, and this leads to increased internal pressure.
FIG. 41 is a schematic diagram illustrating the configuration of a process cartridge comprising a developing device, and the internal pressure increasing phenomena described above will be described with reference to this drawing. With the developing device 4000B disposed within the process cartridge 4000A shown in FIG. 41, in the event that a developing sleeve 4000B1 rotates in the direction indicated by the arrow in the drawing, the residual toner 4000T0 on the perimeter of the developing sleeve 4000B1 which has passed the developing region where the magnetic brush is made to face the photosensitive member 4000C and to come into contact therewith, moves along with the rotations of the developing sleeve 4000B1. The residual toner 4000T0 falls off of the developing sleeve 4000B1 due to the repelling magnetic filed due to magnets 4000D1 and 4000D2 of the same polarity which are disposed within the developing sleeve 4000B1.
On the other hand, a screw member 4000E for drawing up the stirred developing agent to the developing sleeve 4000B1 is provided near the developing sleeve 4000B1, and the surface layer air which moves along with the rotations of the screw member 4000E is concentrated a the position where the toner is repelled and falls off of the developing sleeve 4000B1. Accordingly, at the position where the developing sleeve 4000B1 and the screw member 4000E face one another, the pressure increases due to the density of the air increasing owing to the surface layer air of both being collected at this position, whereby the pressure increases at the range past the developing region in the direction of rotation of the developing sleeve 4000B1. Accordingly, the toner suctioning operations, due to the negative force generated in the downstream direction of motion of the magnetic brush remaining on the developing sleeve 4000B1, are not performed suitably. Consequently, toner scattering preventive actions due to the above-described negative pressure cannot be effectively obtained.
Further, in the event of suctioning the toner past the developing region into the housing of the developing device due to the tendency for the pressure to become negative, suctioning due to negative pressure can be made in the event that all of the toner in the developing agent carried in a bristled state on the surface of the developing sleeve behaves in the same way, but in reality, the behavior in movement differs between the tip of the brush and the surface side of the developing sleeve.
FIG. 42 is a model diagram illustrating the way in which the developing agent moves, passing through the developing region, under negative pressure from the housing side. In FIG. 42, the developing agent which has passed through the developing region moves by being carried by the developing sleeve 4000B1, but there are cases wherein the developing agent at the tip of the brush is scraped off due to the shock of coming into contact with the wall face of the housing facing the developing sleeve 4000B1. The developing agent bristling on the surface of the developing sleeve generates moment in accordance with the rotations of the developing sleeve. Accordingly, the developing agent situated at the tip of the brush is subjected to greater shock at the time of coming into contact with the wall face of the housing as compared to the base side of the brush, so part of the developing agent more readily falls off at the time of being subjected to shock. The toner contained in the developing agent readily falls of and floats upon being subjected to shock in the event that the charge has weakened following passing through the developing region. Such toner may scatter outside from the housing due to the effects of the airflow which will be described alter.
The airflow at the surface of the developing sleeve at the time of the developing sleeve 4000B1 rotating is uniform at the surface of the developing sleeve, but the flow of the air following around at the tip side of the developing agent which is bristling is in a relation opposite to that so far, due to the reactive force (collision force) received upon coming into contact with the wall face of the housing. Particularly, the airflow at the time of coming into contact with the wall face of the housing is the opposite to the airflow at the developing sleeve surface side, also due to effects of the viscosity with the wall face, and the speed thereof may be instantaneously negated.
At the tip of the brush where such a phenomenon is occurring, in the event that there is a tendency for negative pressure to occur a the position that the developing agent, which has passed through the developing region by pumping due to movement of the developing agent, enters the housing, the developing agent flows backwards toward the position that the developing agent enters the housing due to the negative pressing, as shown in FIG. 43 (indicated as airflow blowing out in FIG. 43).
At the position where the developing agent enters the housing, the surrounding air (the airflow denoted by reference numeral 4000PS in FIG. 42) has a tendency to be taken in as shown in FIG. 42, using the pumping action of the developing agent carried on the developing sleeve, so the air taken in mixes with the air moving along with the developing agent reversing direction of flow on the surface of the developing sleeve 4000B1 and readily generates turbulence, so the toner convecting due to this disturbance scatters outside of the housing upon being affected by air moving along with the movement of the photosensitive member (the airflow denoted by reference numeral 4000PS1 in FIG. 42).
Consequently, part of the toner contained in the developing agent which has passed through the developing region may scatter again from the housing, leading to a situation wherein the reduction in pressure to prevent scattering may instead cause scattering of toner.
Accordingly, the present invention has been made in light of the background in which various technical problems exist, and it is a first object thereof to provide a developing device and an image formation apparatus whereby effects of suppressing scattering of toner which occurs at the upstream side of the developing region as described above can be improved.
Also, it is a second object of the present invention to provide a developing device, an image formation apparatus, and a process cartridge wherein scattering of toner which occurs at the downstream side of the developing region can be suppressed in a stable manner.